1. Field of the Invention
This invention relates to a sheet for measuring ultrasonic waves, which can be used for measuring the ultrasonic wave strength distribution of ultrasound used in ultrasonic medical diagnostic equipment, ultrasonic medical treatment equipment and the like.
2. Prior Art
It is important to know the sound field distribution and strength of ultrasound emitted by, for example, an ultrasonic medical diagnostic apparatus to clearly see the effects of ultrasound on the body and to evaluate the performance and safety of the ultrasonic medical diagnostic apparatus.
Furthermore, with an ultrasonic treatment apparatus, it is necessary to beam concentrated ultrasonic waves at a diseased area, and so it is also necessary to check what kind of irradiation characteristics the oscillating device used for treatment has. Furthermore, even if desired characteristics are obtained at a specific frequency, there is a possibility that at other frequencies the characteristics will be different, and so it is necessary to ascertain the characteristics at various frequencies.
Various methods for measuring the strength and strength distribution of ultrasonic waves have been known.
For example, by disposing an ultrasonic microphone in a liquid being irradiated with ultrasonic waves, the strength of the ultrasonic waves in the position in which the ultrasonic microphone is disposed is measured. Also, by changing the position of the ultrasonic microphone, it is possible to measure the strength distribution of the ultrasonic waves.
However, there are the following problems with the measuring method using an ultrasonic microphone: (1) Because an ultrasonic microphone having a certain volume is disposed in a liquid, the ultrasonic wave distribution is disturbed by the presence of the ultrasonic microphone itself, making accurate strength distribution measurement impossible. (2) Because the frequency band of an ultrasonic microphone is generally small, it is not possible to measure the strength distribution of ultrasound extending over a wide frequency range. (3) Because ultrasonic microphones generally have specific directional characteristics, measurement results vary depending on the attitude in which the ultrasonic microphone is disposed. (4) The characteristics of an ultrasonic oscillating device cannot be ascertained intuitively from measured numerical data, and it is necessary to plot the data on a graph or otherwise process it. (5) To measure an ultrasonic wave distribution in real time it is necessary to deploy multiple ultrasonic microphones, but since ultrasonic microphones are very expensive it is difficult to provide a large number of them.
In addition to the measuring method using an ultrasonic microphone as described above, there are also optical methods such as the Schlieren method wherein fluctuation in refractive index caused by ultrasonic wave irradiation is detected optically. With this optical method, it is possible to make visible and to measure sound field strength distribution without the measuring equipment itself disrupting the state of the sound field being measured. However, the optical method has the problem of requiring an image-forming optical system, including a special light source, lenses and the like. Furthermore, the measuring apparatus is quite large.
Also known is a method of utilizing an acoustic luminescence phenomenon wherein certain substances become luminous slightly when they are irradiated with ultrasonic waves, and the 3-dimensional distribution of ultrasonic waves is measured by extended-exposure photography. However, because this method does not allow direct viewing, one must carry out the photography and developing before viewing the results. This all takes a lot of time.
Accordingly, an object of this invention is to provide a sheet for measuring ultrasonic waves with which it is possible to easily measure a 2-dimensional ultrasonic wave distribution.